1. Technical Field
The present invention relates to a technique which reads an output of a light-receiving element such as a photodiode.
2. Related Art
In recent years, a display panel in which liquid crystal elements or organic EL elements are arranged in a matrix shape has been widely been used for an electronic apparatus such as a cellular phone, a personal digital assistant, or the like. The display panel is used under various circumstances, for example, under bright conditions where there is sufficient sunlight, that is, daytime, or under dark conditions where external light is insufficient, that is, night. For this reason, when brightness or image quality of a display element is constant irregardless of external light, there is an inconsistency in that, while the display panel can be easily viewed under some conditions, it can hardly be viewed under other conditions. Accordingly, in such a display panel, it is preferable to detect external light and control the brightness or image quality according to the detection result.
In such a control, a light-receiving element such as a photodiode is used to detect external light. In this case, however, if the light-receiving element is provided separately from the display panel, a space for mounting the light-receiving element is required extra in the electronic apparatus. Further, an opening portion needs to be provided in the light-receiving element to detect external light.
As a countermeasure against the above-described problems, a technique in which, in the display panel, light-receiving elements are formed by using the same process as that of a thin film transistor (hereafter, suitably referred to as ‘TFT’) for switching a pixel in the display panel, such that the display panel itself detects external light, has been proposed.
In this technique, the detection precision of light amount is degraded due to the noise mixed into an output line. Accordingly, a technique in which the noise present on the output line is detected and the detected noise is supplied to the output line after being inverted, such that the noise present on the output line is corrected, has been proposed (see Japanese Unexamined patent Application Publication No. 9-82931 (FIG. 1)).
However, when the light-receiving element is formed with the same process as that of the thin film transistor for switching the pixel in the display panel, the detection precision of light amount is degraded due to the noise or dark current by the light-receiving element itself.